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FOUS30 KWBC 311429
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1029 AM EDT FRI JUL 31 2015
...VALID 15Z FRI JUL 31 2015 - 12Z SAT AUG 01 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...
SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
65 SSW ABQ 15 NW TCS 35 WNW SVC 35 NNW SAD 50 SSW SOW 15 SW SOW
10 E SJN 30 SSW RQE 30 NNW RQE 30 SW FMN 20 SSE CEZ 10 N CEZ
20 S MTJ 30 N CPW 30 SSE ALS 35 NW CAO 10 NW PYX 15 NNW CSM
20 SSE HBR 30 SE CDS 25 ENE PVW 30 N CVN 20 ESE CQC 65 SSW ABQ.
...SOUTHWEST STATES INTO THE TX/OK PANHANDLES AND WESTERN OK...
MONSOONAL MOISTURE REMAIN IN PLACE OVER THE SOUTHWEST STATES...AND
SOME OF THE DEEP MOISTURE IS BEING DIVERTED INTO THE SOUTHERN
PLAINS ALONG A FRONTAL BOUNDARY. THE DEEP MOISTURE...COMBINED WITH
MARGINAL TO MODERATE INSTABILITY...COULD RESULT IN ORGANIZED
CONVECTION WHICH PRODUCES HEAVY TO EXCESSIVE RAINFALL...ESPECIALLY
IN THE LATE NIGHT / EARLY MORNING HOURS.
EARLY THIS MORNING A SLOW MOVING MCS WAS PRODUCING HEAVY RAIN IN
THE OK/TX PANHANDLES. THIS IS LIKELY TO DISSIPATE OR BECOME
FRAGMENTED AS THE BOUNDARY LAYER RESPONDS TO MIXING...AND IN THE
ABSENCE OF ANY SUSTAINED INFLOW. DOWNSTREAM A SMALL NORTHERN
STREAM SHORTWAVETROUGH WAS ANALYZED TO BE DROPPING INTO NORTHERN
OKLAHOMA...AND ISOLATEDCONVECTION WAS SEEN OUT AHEAD OF THIS
FEATURE IN THE INSTABILITY AXIS ACROSS CENTRAL OK. THE MODELS
APPEARED TO BE OVER-FORECASTING THE COVERAGE AND EFFICIENCY OF
THIS ACTIVITY...LIKELY OWING TO MARGINAL INSTABILITY AND WEAK WIND
FIELDS. THUS...CONVECTION SHOULD MAINLY BE SCATTERED...WITH ONLY
SMALL SCALE DOWNPOURS THROUGH THIS AFTERNOON.
THE LOW LEVEL FLOW INCREASES ACROSS WEST TX INTO WESTERN OK AND
WESTERN KS AFTER 01/00Z...THOUGH THERE IS SOME SPREAD CONCERNING
JUST HOW STRONG IT GETS. ASSUMING A 20 KNOT LOW LEVEL INFLOW INTO
NORTH TX...A SMALL MCS COULD DEVELOP AFTER 01/06Z THERE...AND
CONTINUE EAST SOUTHEAST ALONG THE DIFLUENT THICKNESS PATTERN INTO
SOUTH CENTRAL OK BEFORE 01/12Z. THE MOISTURE IS DEEP ENOUGH FOR
HIGH RAINFALL RATES WITH THE MCS...SO AN AREA OF 1.50 TO 2.00
INCHES OF QPF WAS PLACED OVER NORTH TX AND NEARBY WESTERN OK.
WHILE THE QPF VALUES ARE BELOW THE THREE HOUR FLASH FLOOD GUIDANCE
VALUES...THE POTENTIAL FOR HIGH RAINFALL RATES SUGGESTS THE
POTENTIAL FOR FLASH FLOODING. ACCORDINGLY...A SLIGHT RISK WAS
EXTENDED FROM NORTHEAST NM (WITH THE MCV) INTO NORTH TX AND A
PORTION OF WESTERN OK.
FARTHER WEST...THE MONSOONAL FLOW CONTINUES ACROSS AZ/WESTERN NM.
THERE IS A MULTI MODEL SIGNAL THAT A SHORT WAVE IN THE MID LEVEL
SOUTHERLY FLOW UNDER THE RIDGE COULD CROSS AZ DURING THE SECOND
HALF OF THE PERIOD. THAT COULD ENHANCE LIFT ACROSS EASTERN
AZ/WESTERN NM...ALLOWING CONVECTION TO FORM OUTSIDE OF THE
TERRAIN. ADDITIONALLY...NORTHERN STREAM SHORTWAVES ARE FORECAST TO
ONCE AGAIN FOCUS UPPER LEVEL DIFULENCE OVER NORTHERN NM LATE IN
THE NIGHT...AND A BROAD SLIGHT RISK OF EXCESSIVE RAINFALL WAS
MAINTAINED...STRETCHING FROM EASTERN AZ INTO SOUTHERN CO AND ON
INTO TX/OK.
IN SOUTHWEST AZ...THE HIGH MOISTURE CONTENT AIR (WITH PRECIPITABLE
WATER VALUES TOPPING OUT NEAR 1.75 INCHES) COULD ALLOW FOR LOCALLY
HEAVY RAINFALL...ESPECIALLY BY LATE EVENING AND OVERNIGHT AS THE
NEXT SHORTWAVE APPROACHES OUT OF MEXICO...AND IF OUTFLOWS CAN
PROVIDE LOW LEVEL ASCENT. HOWEVER...AT THIS POINT...IT IS UNCLEAR
JUST HOW WIDESPREAD THE HEAVIER RAINFALL WILL BE...SO FOR NOW NO
SLIGHT RISK AREA WAS ASSIGNED.
...SOUTHERN NEVADA AND ADJACENT AZ/CA...
MID LEVEL RIDGING WAS CENTERED OVER THE PLAINS AND EASTERN PART OF
THE FOUR CORNERS REGION. THIS WILL CONTINUE TO ALLOW WEAK INVERTED
TROUGHS TO LIFT UP THROUGH THE LOWER PART OF THE COLORADO RIVER
BASIN TOWARD CALIFORNIA. ONE SUCH FEATURE WAS ANALYZED OVER
CENTRAL AZ THIS MORNING IN THE 500 MB DATA...AND IS FORECAST BY
THE RAP TO LIFT NORTHWEST...EXTENDING FROM THE SOUTHERN SIERRAS
BACK ACROSS SOUTHERN NEVADA THIS AFTERNOON. THIS SHOULD PROVIDE
SOME LIFT AND SLIGHTLY ENHANCED WIND FIELDS TO MAKE THE MOST OF
WHAT WILL BE MARGINAL INSTABILITY GIVEN RELATIVELY DRY LOW LEVELS
AND PRECIPITABLE WATER VALUES FAIRLY TYPICAL OF AN AVERAGE MONSOON
DAY. WITH VERY SLOW CELL MOTIONS...RAIN RATES MAY EXCEED AN INCH
IN AN HOUR...AND A FEW SMALL SCALE INSTANCES OF HEAVY RAIN AND
FLASH FLOODING ARE POSSIBLE.
...COASTAL SC/GA/FL...
HIGH RESOLUTION MODELS ARE MOST EMPHATIC ABOUT A HEAVY RAIN
MAXIMUM FORECAST NEAR THE COAST OF WESTERN FLORIDA WEST OF
GAINESVILLE. THE BULK OF THIS EVENT IS LIKELY TO PROPAGATE
OFFSHORE...HOWEVER...MOVING INTO THE INFLOW AFTER INITIATING ALONG
THE SEA BREEZE. VERY HEAVY RAIN RATES MAY OCCUR INITIALLY...EARLY
THIS AFTERNOON...GIVEN DEEP AND ANOMALOUS MOISTURE. A MORE
INTRIGUING POSSIBILITY FOR HEAVY RAIN LEADING TO FLASH
FLOODING...IS ALONG AND JUST INLAND OF THE COASTS OF SOUTH
CAROLINA AND GEORGIA. MORNING SOUNDINGS FROM CHARLESTON AND
JACKSONVILLE WERE VERY MOIST...AT OR ABOVE 2 INCH PW...WITH LAPSE
RATES SUPPORTIVE OF VERY DEEP CONVECTION AND NO PARTICULARLY
STRONG SUBSIDENCE LAYERS. THUS...THE HIGH PW MAY BE COUPLED WITH
STRONG CAPE...AND MEAN 0-6 KM STEERING WINDS ARE NEAR ZERO KNOTS
OVER A LARGE SWATH FROM SC TO NORTHERN FL. MESOSCALE MODELS ARE
EVENLY DISTRIBUTING THE PRECIPITATION IN THIS AREA...BUT IT WOULD
NOT BE SURPRISING TO SEE A FEW CELL MERGERS OR STATIONARY CELLS
WHICH PRODUCE ISOLATEDRAINFALL OF 3 TO 4 INCHES IN A SHORT TIME.
BURKE/HAYES
$$